Radiant heating systems for living and/or working spaces are widely known. One popular type of radiant heating system for these applications is the hydronic heating system wherein a heated fluid such as water is pumped through an endless pipe loop installed under a floor (RFH) or inside a wall (RWH). Heat is supplied to the living or workspace by radiation from fluid circulated through the endless loop which heats the floor or wall. The fluid is typically heated by a boiler which burns a carbonaceous fuel such as natural gas or fuel oil.
Traditionally, hydronic heating coils have been installed between floor joists or wall studs with at least one loop between each pair of adjacent joists or studs. Furthermore, the endless loop has traditionally been supported in close contact with the floor or wall surface and heat conductive plates have been used to enhance the radiation of heat from the endless loop to the undersurface of the floor. Typical of the prior art installations are Canadian Patent Application 2,078,135 entitled RADIANT FLOOR AND WALL HYDRONIC HEATING SYSTEMS to Fiedrich which was laid open to public inspection on Dec. 31, 1993; and Canadian Patent Application 2,063,841 entitled MODULAR BACK SIDE RADIANT HEATING PANELS to Bourne and Springer which was laid open to public inspection on Sep. 26, 1992.
In Canadian Patent Application 2,078,135, a heating system using plastic tubing for RFH and RWH heating applications is described. The system uses a thermally conductive plate that is mounted under the floor or behind the wall directly adjacent and undersurface of the floor or wall. In one embodiment, a radiation plate made of aluminum or the like has a longitudinal groove 34 that fits snugly around the plastic tubing. The tubing is installed under the floor by cradling it in the groove of the conductive plate, and the plate is screwed to the sub floor using strapping to hold the plate and the tubing in close contact with the sub floor surface. The entire installation is accomplished with a single endless loop of tubing.
Canadian Patent Application 2,063,841 describes modular heating panels constructed with plastic pipes supported on an insulated backing intended to be clamped between floor joists and/or wall studs for RWH and RFH hydronic heating systems. Each panel is constructed of an insulating board and aluminum heat fins. The heat fins completely surround the pipe and provide a heat radiating surface with a large surface area which is preferably held in close contact with the subfloor or rear wall surface. The plastic heating pipes are pre-installed in each panel and must be connected together to assemble an endless heating loop.
Such prior art radonic heating systems suffer from a number of disadvantages. First, the radiant plates which support the heating tubes are preferably secured directly to the floor or wall surface. This promotes "hot spots" on the floor or wall. Heating fluid temperatures must therefore be controlled in order to prevent hot spots which could prove injurious or discomforting to occupants of the heated space. Second, plastic piping used in hydronic heating system is vulnerable to puncture by fasteners driven through the flooring or the wall structure by persons who are not aware of the hazard. Such accidental damage to the heating system can cause water damage and potentially cause damage to the fluid distribution pump and/or the boiler used for heating the fluid. Third, at least one loop is required in each inter joist space in order to lay out the endless heating loop efficiently as well as to provide adequate radiant heat in most climates. Fourth, as noted above most boilers operate at temperatures which exceed the desired temperature of a floor surface. It is therefore necessary to provide some mechanical arrangement to prevent fluid heated by the boiler from circulating in an undiluted condition through the hydronic heating system. Expensive flow control components which must be installed by skilled workmen are therefore required in the heating system. This contributes to the cost of installation and maintenance of the system.
FIGS. 1a-1e illustrate several commonly used prior art mechanical arrangements for controlling the temperature of fluid circulated through hydronic floor heating systems. In FIG. 1a, a boiler bypass valve 20, typically a balancing valve, is placed between a supply and a return side of a boiler 28. A second valve may be required on the return side of the boiler 28 to help restrict flow through the boiler 28. When the system calls for heat, the pump pulls a portion of the water through the boiler 28 and a portion from the water returning from the floor. The returning water mixes with the boiler water and lowers the temperature of the boiler water. The resulting water temperature depends upon the mix ratio. Cooler water may be procured by opening the bypass valve to permit more water from the floor to recirculate. This system is primarily useful when a fixed temperature is desired and there is no variation in the flow rate of heating fluid in the distribution pipe.
FIG. 1b shows an alternate arrangement wherein a three-way mixing valve 30 is used to do essentially the same job as the boiler bypass valve 20 described above. The three-way mixing valve 30 is mounted inline on the supply side of the boiler with a connecting line to the return side of the boiler 28. By manually adjusting the valve, a mixture of boiler water and return water can be balanced to the desired floor delivery temperature. In an alternate three-way mixing valve arrangement, a tempering valve may be used. The tempering valve is plumbed in the same manner as the three-way manual valve that is designed to produce a constant temperature. The tempering valve has an internal thermal element which throttles the amount of return water that is allowed to mix with the boiler water. The thermal element is manually adjusted to a desired temperature and will maintain a water mixture suitable to attain the desired temperature at all times when the system is operational.
FIG. 1d shows yet another common arrangement using a four-way mixing valve 34. It is desirable to maintain a constant flow in the boiler in order to increase boiler life and efficiency. The four-way mixing valve 34 makes this possible. It is positioned between a primary circulation loop between the boiler and a primary circulation pump 36 and a secondary installation loop between a heating loop 26 and a circulation pump 24. The boiler water and water returning from the floor are proportionally mixed to the desired floor delivery temperature and circulated back to the floor. Some of the returning floor water is also mixed with the recirculating boiler water and returned to the boiler 28. Flow in both of the loops is kept constant. The high water temperature return to the boiler reduces the probability of stressing the boiler with cold shock and condensation.
FIG. 1d shows another arrangement wherein a buffer tank 38 is used to reduce the boiler water temperature before it is circulated through the heating loop 26. A first pump 36 circulates water between the boiler 28 and the buffer tank 38. The buffer tank typically holds 20 to 50 gallons of water. The boiler is controlled by a water temperature thermostat (not shown) placed in the top of the buffer tank which senses the water temperature in the tank. A second pump 24 circulates water from the tank through the heating loop 26. The second pump draws water from the top of the buffer tank as called for by a room temperature thermostat (not shown) and returns water to the bottom of the buffer tank.
FIG. 1e shows yet another arrangement wherein a heat exchanger permits a boiler water loop to be completely isolated from the heating loop 26. Heat exchanger constructions are well known. They may be a tube type or a shell and plate type construction. In either case, water heated by the boiler is circulated in close contact with water circulated to the heat loop 26. Heat exchangers must be properly sized and the flow, exchange rate and BTU output of the boiler are critical in designing a system that will perform properly. Heat exchangers are generally compact but relatively expensive and are best configured by technicians that specialize in heat exchangers for hydronic heating systems.